Many types of transmissions are capable of operating at variable speeds. Typically, a variable-speed transmission includes a means for adjusting speed in response to control by an operator using a machine comprising the transmission. One type of transmission utilizes one or more variable-pitch pulleys to enable speed variation. As generally known to persons skilled in the art, a variable-pitch pulley typically includes two plates defining a groove therebetween for carrying a belt driven by a motor. One of the plates is axially movable relative to the other, such as along a central hub, while the other plate remains fixed in position to a shaft about which the plates of the pulley rotate. Cams or other means are employed to cause the movable plate to move toward or away from the other plate, such as by changing the tension in the belt, thereby varying the pitch of the pulley (i.e., widening or narrowing its groove) and enabling the belt to move away from or toward the shaft (i.e., running the belt at a shallow or deep position within the groove). The speed of the shaft changes in response to the change in position of the belt within the groove defined between the plates. Examples of the use of variable-pitch pulleys are disclosed in U.S. Pat. Nos. 4,322,934; 4,653,345; 4,924,988; and 6,186,916; and U.S. Patent Application Pub. No. US 2002/0183145.
While variable-pitch pulleys often perform well in cooperation with transmissions for the conventional purpose of varying speed between minimum and maximum values, such pulleys are not capable of providing a complete and/or effective engagement or disengagement of the torque supplied to the transmission. In one approach disclosed in U.S. Pat. No. 4,322,934, a transmission is powered by a motor and includes a belt-driven variable-pitch pulley. The motor is, in a sense, “disengaged” from the transmission by decreasing tension on the belt driving the variable-pitch pulley to such a degree that the belt can no longer drive the pulley. This approach can cause the belt to prematurely wear due to slippage on the surfaces of the pulley and the repeated cycling of the belt between extreme tensioned and relaxed states. Moreover, additional driving components such as extra pulleys and belts are required so that other operative components driven by the motor, such as blades in the case of a lawnmower, are not affected by the slackening of the variable-pitch pulley's belt.
In other approaches, the function of engagement/disengagement has required the use of a separate transmission component dedicated for that purpose, such as a cone clutch, dog clutch, ratchet, brake, pressure plate or friction disk assembly, or the like. Moreover, separate control mechanisms have often been required to enable an operator to control engagement/disengagement and speed variation. Examples include transmissions disclosed in U.S. Pat. No. 6,186,916 and U.S. Patent Application No. US 2002/0183145. In these two references, the pitch of a variable-pitch pulley is changed by rotating a cam device, while maintaining tension in the belt driving the pulley. Such transmissions require a separate clutch to effect engagement and disengagement.
In another example, U.S. Pat. No. 4,653,345 likewise discloses a transmission in which a variable-pitch pulley is adjustable by rotating a cam device. In addition, the transmission of U.S. Pat. No. 4,653,345 includes a separate, internal shifting assembly disposed within the transmission's housing, remotely from the variable-pitch pulley. The shifting assembly switches the transmission between driving and neutral states. A control lever is connected both to the rotatable cam device and, through a linkage assembly, to the shifting assembly. Rotation of the control lever actuates both the cam device and the shifting assembly. The variable-pitch pulley and the shifting assembly are separate devices, require a relatively large number of components, and involve a degree of complexity and cost unsuitable for many types of commercial applications.
It would therefore be advantageous to provide a control apparatuses and methods for use with a transmission that integrally combines the functions of both selective coupling and speed variation, thereby eliminating the number, complexity, and cost of transmission components required for the transmission.